Thermionic tube



I Feb. 3 1931. F, s, McCULLOUGH 1,791,140

THERMIONIC TUBE Filed July 1'7, 1925 2 Sheets-Sheet 1 ZZYZ/EZYZUJ". Fredzrzbir 5! 5E ZZZ/112072 iii/T275 57 F 1931. F. s. MGCULLOUGH 1,791,140

THERMI ONI C TUBE Filed July 17, 1925 2 Sheets-Sheet 2 fmimrkjfif ZZZ/011g];

$47 WW EZZFFIFM Patented Feb. 3, 1931 UNITED STATES PATENT OFFICE THERIIONIC TUBE Application filed my 11, 1925. Serial r. 44,162.

This invention relates to thermionic tubes such as are used in radio telephony and telegraph and pertains specifically to that type of tu wherein the cathode is heated or energized by the application of an alternating current.

In almost all alternating current tubes the cathode is an equi-potential surface and for this reason such tubes display markedly dif ferent characteristics from the well known tube in which the cathode is a filament energized by direct current. The invention herein set forth is to eliminate the equi-potential surface and make the tube act similar to a direct current gradient filament by a new method.

The present invention has for its principal object to provide an alternating current tube of such nature and construction that all of the valuable electrical characteristics of a direct current tube are attained especially with respect to the control of the potential of the grid with respect to the cathodes.

T accomplish the above noted very desirable results by employing. a pair of independent cathodes, heated by a heating element which is common to both cathodes. This heater may be adapted to energize the cathodes by induction or by conduction.

in the figures, which accompanying and form a part of this specification and in which like reference numerals designate corresponding parts throughout:

Fig. 1 is a partially sectioned elevation of one embodiment of my improved tube.

Fig. 2 is an enlarged view of the cathodes and heater.

Fig. 3 is a diagrammatic representation of a simple regenerative receiving circuit utilizing my improved tube.

Fig. 4 is an enlarged view of a modified form of a heater and cathode element adapted for use with my tube.

Fig. 5 is an enlarged view of a second modified form of a combined heater and cathode element for use with my tube, and

Fig. 6 is an enlarged end view of the device of Fig. '5. 4

Referring now to Figs. 1 and 2, my improved tube comprises as usual a glass envelope (1) provided with a stem in each extremity as indicated. The upper stem permits egress of the heater leads (5 and 6) which are connected to contact studs (2 and 3) respectivel which are carried in an insulating cap (4 The cap (4) is secured in the usual manner to the glass envelope (1) The heating or resistance unit (7) may be of tungsten or tungsten alloy and is preferably formed to have an acute angle at its lower apex. Thin tubes (8 and 9) preferably of porcelain, are slipped over the heater wire and are preferably maintained with their lower extremities in contact as shown in Fig. 2. The cathodes (10 and 11) are carried by the tubes (8 and 9) respectively and are so relatively maintained by the tubes as to be at all times out of contact with each other. These cathodes are formed of nickel or nickel alloy and are coated with any of the well known substances of high electron emissivity at lowtemperatures. Cathode (10) is connected through conductor (12) and thence through the lower stem in the envelope (1) with stud (23), while cathode (11) is con nected through conductor (13) with stud (22) These two studs are carried by an insulating base (20) which in all respects is similar to the standard base used in direct current tubes and the studs (22 and 23) correspond in position and location to the studs in a standard base to which the filament cathode leads are connected and which make contact through a standard socket with the positive and negative terminals of a direct current battery. A grid (14) surrounds the cathodes (10 and 11) and is supported by standards (17 and 17 one of which (17) extends through the press in the lower stem and is connectedto stud (21). This stud is the counterpart in location to the stud to which the grid is connected in a standard base. A plate or anode (15) likewise surrounds both the grid (14) and the cathodes (10 and 11) and is supported by standards (16 and 19) the standard (19) passing through the press and being connected to stud (24) which corresponds to the plate stud in a standard base.

Referring particularly to Fig.4, I here show. a modification com rising a porcelain tube which is provi ed with a air of longitudinally extending orifices t rough which the heating or resistance wire 51 extends. The heatin wire 51, of course, is connected through'tile upper seal to the terminals 2 and 3. Surrounding the. element 50 .isa pair of cathodes 52 and 53. These cathodes are connected by conductors 54 and 55 to the terminals 22 and 23 in the base 20.

Referring more particularly to Figs. 5 and 6, I here show a second modification comprising a porcelain tube .60 having a pair or orifices through which the heatin or resistance unit 61 extends and the heating unit 61 is adapted to be connected through the upper seal to the terminals 2 and 3. I also provide a pair of semi-cylindrical cathodes 62 and 63 partially surrounding the porcelain tube 60, and the cathodes 62 and 63 are connected by conductors 64 and 65 through the lower press to the contacts 22 and 23 in the base 20.

The functioning of my tube with either the element shown in Fig. 4 or Fig. 5 is substantially the same as for the element shown in Fig. 2.

It will be observed from the foregoing description that my improved alternating current tube comprises two independent cathodes heated by a heater common to them; that each cathode is provided with a separate stud in the base and that these studs are so located as to correspond with the filament studs in an ordinary direct current tube. Therefore, if my tube be inserted in a standard socket to which a battery is connected as in the usual Way, the circuit conditions will be as represented in Fig. 3, which shows in diagram a three coil regenerative radio receiver, comprising the antenna 100, antenna inductance 101, grid inductance 103, tickler coil 102 and earth 104:. As is usual the battery 105 is provided with a potentiometer 106, the contact arm of which is connected to the grid coil 103, and thence to the grid 14. My improved cathodes (10 and 11) are shown connected to the positive and negative terminals respectively of the battery 105 while the plate 15 is connected through the tickler or feed back coil 102 with a head phone 108 and thence to the positive terminal of a B battery 107, the negative terminal of which is connected to the negative terminal of the battery 105 and to cathode 11.

The extreme simplicity of. my improved tube and its adaptability to function in all respects similarly to the ordinary direct current tube will be obviousfrom Fig. 3. It will be observed that cathode 10 is connected to the positive terminal of the battery 105 and will thus be at positive potential while similarly cathode 11 will be at negative potential, a condition found in the direct current type of tube in which the cathode is a filament. It will further be observed that by moving the contact on the potentiometer the grid may be biased either positive or negative or zero with infinite accuracy of adjustment as in the circuits using direct current tubes.

While I have illustrated certain embodi-' g tube, a cathode comprising a pair of separate independent cathode elements of substantially the same size, a refractory rod extending through each cathode-element, heating means common to said elements including a resistance wire extending serially through said refractory rods for rendering said cathode elements electronically active, independent external connections for each of said cathode elements, and a battery bridged across said external connection.

2. In an alternating current thermionic tube, a pair of separated cathodes, a heater common to said cathode, a grid and plate cofunctionally related to both of said cathodes, a standard contact base, said grid and plate being connected to the grid and plate contact respectively in said base, one of said cathodes being connected to one filament contact in said base while the other cathode is connected to the remaining filament contact.

3. In an alternating current thermionic tube, a pair of independent cathodes includ ing tubular members'and insulating members within the tubular members, a grid and plate co-functionally related to both of said cathodes, a common heater for said cathodes extending through said insulating'members, a standard terminal base, said grid being connected to the grid stud in said base, said. plate being connected to the plate stud in said base, one of said cathodes being connected to a filament stud in said base and the other of said cathodes being connected to the remaining filament stud in said base, and a member having contacts connected to said heater.

4. In an alternating current thermionic tube, a pair of separate tubular cathodes, heating means common to and independently extending through said cathodes, a grid and plate encircling said cathodes, a terminal base carrying contact studs for said grid, plate and cathodes each of said cathodes being each connected to an independent stud in said base.

5. In an alternating current thermionic tube, a pair of tubular cathodes having electron emitting surfaces, a heating means extending independently through said tubular cathodes for rendering said electron emitting surfaces active, a grid and plate surrounding and co-functiona-lly related to said cathodes, a terminal base having contacts to which said grid and plate are connected, and a pair of separate contacts to which said cathodes are respectively connected.

6. A thermionic amplifier including a pair of tubular cathodes, having separate electron emitting members, refractory rods extending through said members, a heater Wire extending serially through said refractory rods for heating said tubular cathodes to render the same active, a grid around said cathode, an anode around said grid, and means including a battery bridged across said cathodes for oppositely potentializing said cathodes.

7. A thermionic amplifier comprising a pair of cathodes including electron emitting members, insulating means within said members, a single heating element for said cathodes extending through said insulating means,

. a grid element and an anode co-functionally related with said cathodes, said electron emitting members being so positioned with respect to said anode that the electrons emitted by said members are equally effective in the functioning of the amplifier, and means for supplying said cathodes with opposite potentials from a battery bridged across said cathodes.

8. A thermionic amplifier including a pair of independent cathodes adapted to emit electrons, refractory means within said cathodes, an alternating current heating element extending serially through said cathodes for heating the same, an anode surrounding said cathodes and equidistant from said cathodes,

a grid positioned between said cathodes and said anode, a battery bridged across said cath odes for potentializing the same, a base for said amplifier, and contacts for said base connected to said cathodes, grid and anodes. Signed by me at Chicago, county of Cook and State of Illinois, this 15 day of July, 1925.

FREDERICK S. MCCULLOUGH. 

